Acute carbon monoxide poisoning has frequently occurred in Korean, because of the coal briquette being widely used as fuel in Korean residences. Carbon monoxide poisoning has been extensively studied, but it ha been sparsely reported that pulmonary edema may develop in acute CO poisoning. We have noticed nine cases of pulmonary edema in acute CO poisoning last year. Other possible causes of pulmonary edema could be excluded in all cases but one. The purpose of this paper is to describe nine cases of pulmonary edema complicated in acute CO poisoning and discuss the pathogenesis and the prognosis.